Calculate roof snow load from snow depth and roof size with typical snow densities, or find the ASCE 7 balanced load or the depth that hits a load limit.
Roof Snow Load Formula
For measured snow, this calculator uses vertical depth over the horizontal roof footprint. With depth d in inches and snow density D in lb/ft³:
Snow load (psf) = (d / 12) × D Total snow weight (lb) = horizontal footprint (ft²) × snow load (psf)
Pitch can increase the sloped roof surface area, but does not increase snow volume again when depth is already vertical. If depth was measured perpendicular to a sloping roof, convert it to vertical depth first. Preset densities are estimates; measured snow-water equivalent or density is preferable when available.
ASCE 7-22 and 7-16 Are Different
ASCE 7-22 uses risk-targeted ground snow loads. Its balanced flat-roof component is pf = 0.7 × Ce × Ct × pg; the selected risk category is represented by pg, so a separate snow importance multiplier is not added. Legacy ASCE 7-16 uses pf = 0.7 × Ce × Ct × Is × pg. Both modes calculate ps = Cs × pf using the slope factor you supply.
Use mapped ground load and verified exposure, thermal and slope factors from the same locally adopted edition. In 7-22, thermal factors for heated roofs can depend on roof insulation and ground snow load, and slope-factor provisions also changed. The calculator prefills typical values of 1.0 for Ce, Ct and Cs; replace them with the verified factors for your roof. An optional applicable minimum can be compared with ps, but its applicability must be determined separately.
This calculates a balanced-load component only. It does not complete minimum-load, rain-on-snow, drifting, unbalanced loading, partial loading, sliding snow, load-combination or structural-capacity checks. A higher result from one comparison is not necessarily the governing design load.
Example Calculations
A 40 ft × 30 ft roof footprint with 12 inches of vertical snow at approximately 15.607 lb/ft³ carries approximately 15.607 psf and 18,728 lb total. A 6:12 pitch gives about 1,342 ft² of sloped surface area, but that is not multiplied into vertical snow volume.
For an illustrative 7-22 balanced-load calculation with pg = 40 psf, verified Ce = 1.0, Ct = 1.2 and Cs = 0.8, pf = 33.6 psf and ps = 26.88 psf. These sample coefficients are not recommendations for a particular roof.
Depth Compared With an Entered Load Limit
Equivalent depth = entered load limit ÷ estimated load per unit of vertical depth. At 250 kg/m³, snow adds approximately 1.3006 psf per inch. An entered 20 psf limit corresponds to approximately 15.38 inches, but 20 psf is merely an example and is not a default safe capacity for a home. Other loads, weakened framing, drift concentrations, ice and density variation can invalidate that comparison.
Frequently Asked Questions
Does this tell me whether my roof is safe?
No. It estimates snow weight and performs a stated load comparison. Roof capacity and all relevant loads require a qualified assessment. Do not climb onto a snow-loaded roof to obtain measurements or remove snow.
Is ground snow load the same as roof snow load?
No. Ground load is mapped using the selected standard’s hazard method. Roof load depends on additional conditions and code checks. Older 50-year ground-load data and newer risk-targeted data must not be mixed with coefficients from different editions.
What if the roof shows distress?
Sagging, cracking, unusual noises, or doors and windows that suddenly bind can warrant leaving the affected area and contacting local emergency services or a qualified structural professional. Do not treat a low calculator result as evidence that a distressed roof is safe.
Sources
Method and scope reviewed October 20, 2026: ASCE/SEI 7-22; ICC training on 2024 IBC / ASCE 7-22 snow provisions; ASCE Hazard Tool.
